Rainfall patterns after fire differentially affect the recruitment of three Mediterranean shrubs

Abstract

In fire-prone environments, the "event-dependent hypothesis" states that plant population changes are driven by the unique set of conditions of a fire (e.g., fire season, climate). Climate variability, in particular changes in rainfall patterns, can be most important for seeder species, since they must regenerate after fire from seeds, and for Mediterranean shrublands, given the high yearly variability of rainfall in these ecosystems. Yet, the role of rainfall variability and its interaction with fire characteristics (e.g., fire season) on plant populations has received little attention. Here we investigated the changes in seedling emergence and recruitment of three seeder species (<i>Cistus ladanifer</i>, <i>Erica umbellata</i> and <i>Rosmarinus officinalis</i>) after fires lit during three different years and at two times during the fire season (early and late in the fire season) to account for potential changes in the soil seed-bank during the year. Three plots were burned at each season, for a total of 18 plots burned during the three years. After fire, emerged seedlings were tallied, tagged and monitored during three years (two the last burning year). Rainfall during the study period was rather variable, and in some years was well below average. Seedling emergence after fire varied by a factor of 3 to 10, depending on the species and on the burning year. The bulk of seedling emergence occurred in the first year after fire, and seedling recruitment at the end of the study period was tightly correlated with this early emergence. Seedling emergence in <i>E umbellata</i> and <i>R officinalis</i>, but not in <i>C ladanifer</i>, were correlated with precipitation in the fall and winter immediately after the fire, being <i>E umbellata</i> most sensitive to low rainfall. Fire season was generally not an important factor in controlling emergence and recruitment. We discuss how projected changes in rainfall patterns with global warming can alter the balance of species in this shrubland, and can drive some species to near local extinction

Burning season effects on the short‐term post‐fire vegetation dynamics of a Mediterranean heathland

“…; Moreno et al. ). In this study, seeders (in particular the main species, E. umbellata) were most negatively affected by fire.…”

“…; Moreno et al. ). Further studies are needed to establish the role of regeneration mode in the stability of shrublands to fire.…”

“…Moreno et al. () showed that if the first year after fire is wet, most emergences occur during that year; but if this year is dry, then emergence can occur during the second and third years. In this study, rainfall during the first year after fire was far higher (1472 mm; 95th percentile) than the long‐term average, so it is unlikely that rainfall played a major role.…”

“…Furthermore, similar studies in Mediterranean ecosystems on post‐fire regeneration from the soil seed bank often failed to find significant effects (Moreno et al. ).…”

Burning season does not affect post‐fire regeneration but fire alters the balance of the dominant species in a seeder‐dominated Mediterranean shrubland

“…For seeders, burning season is a significant factor in controlling emergence in some species, but not recruitment 3 yr after fire, suggesting that there is an additional filter (Moreno et al. ). Moreover, this pattern cannot be generalized when differences in fire intensity and other subsequent effects (i.e.…”